using System;
using System.Threading;
using Microsoft.Extensions.Configuration;
using Serilog;
using ZB.MOM.WW.LmxOpcUa.Host.Configuration;
using ZB.MOM.WW.LmxOpcUa.Host.Domain;
using ZB.MOM.WW.LmxOpcUa.Host.GalaxyRepository;
using ZB.MOM.WW.LmxOpcUa.Host.Metrics;
using ZB.MOM.WW.LmxOpcUa.Host.MxAccess;
using ZB.MOM.WW.LmxOpcUa.Host.OpcUa;
using ZB.MOM.WW.LmxOpcUa.Host.Status;

namespace ZB.MOM.WW.LmxOpcUa.Host
{
    /// <summary>
    /// Full service implementation wiring all components together. (SVC-004, SVC-005, SVC-006)
    /// </summary>
    internal sealed class OpcUaService
    {
        private static readonly ILogger Log = Serilog.Log.ForContext<OpcUaService>();

        private readonly AppConfiguration _config;
        private readonly IMxProxy? _mxProxy;
        private readonly IGalaxyRepository? _galaxyRepository;
        private readonly IMxAccessClient? _mxAccessClientOverride;
        private readonly bool _hasMxAccessClientOverride;

        private CancellationTokenSource? _cts;
        private PerformanceMetrics? _metrics;
        private StaComThread? _staThread;
        private MxAccessClient? _mxAccessClient;
        private IMxAccessClient? _mxAccessClientForWiring;
        private ChangeDetectionService? _changeDetection;
        private OpcUaServerHost? _serverHost;
        private LmxNodeManager? _nodeManager;
        private HealthCheckService? _healthCheck;
        private StatusReportService? _statusReport;
        private StatusWebServer? _statusWebServer;
        private GalaxyRepositoryStats? _galaxyStats;

        /// <summary>
        /// Production constructor. Loads configuration from appsettings.json.
        /// </summary>
        public OpcUaService()
        {
            var configuration = new ConfigurationBuilder()
                .AddJsonFile("appsettings.json", optional: false)
                .AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("DOTNET_ENVIRONMENT") ?? "Production"}.json", optional: true)
                .AddEnvironmentVariables()
                .Build();

            _config = new AppConfiguration();
            configuration.GetSection("OpcUa").Bind(_config.OpcUa);
            configuration.GetSection("MxAccess").Bind(_config.MxAccess);
            configuration.GetSection("GalaxyRepository").Bind(_config.GalaxyRepository);
            configuration.GetSection("Dashboard").Bind(_config.Dashboard);

            _mxProxy = new MxProxyAdapter();
            _galaxyRepository = new GalaxyRepositoryService(_config.GalaxyRepository);
        }

        /// <summary>
        /// Test constructor. Accepts injected dependencies.
        /// </summary>
        internal OpcUaService(AppConfiguration config, IMxProxy? mxProxy, IGalaxyRepository? galaxyRepository,
            IMxAccessClient? mxAccessClientOverride = null, bool hasMxAccessClientOverride = false)
        {
            _config = config;
            _mxProxy = mxProxy;
            _galaxyRepository = galaxyRepository;
            _mxAccessClientOverride = mxAccessClientOverride;
            _hasMxAccessClientOverride = hasMxAccessClientOverride;
        }

        public void Start()
        {
            Log.Information("LmxOpcUa service starting");

            try
            {
                // Step 2: Validate config
                if (!ConfigurationValidator.ValidateAndLog(_config))
                {
                    Log.Error("Configuration validation failed");
                    throw new InvalidOperationException("Configuration validation failed");
                }

                // Step 3: Register exception handler (SVC-006)
                AppDomain.CurrentDomain.UnhandledException += OnUnhandledException;

                // Step 4: Create PerformanceMetrics
                _cts = new CancellationTokenSource();
                _metrics = new PerformanceMetrics();

                // Step 5: Create MxAccessClient → Connect
                if (_hasMxAccessClientOverride)
                {
                    // Test path: use injected IMxAccessClient directly (skips STA thread + COM)
                    _mxAccessClientForWiring = _mxAccessClientOverride;
                    if (_mxAccessClientForWiring != null && _mxAccessClientForWiring.State != ConnectionState.Connected)
                    {
                        _mxAccessClientForWiring.ConnectAsync(_cts.Token).GetAwaiter().GetResult();
                    }
                }
                else if (_mxProxy != null)
                {
                    try
                    {
                        _staThread = new StaComThread();
                        _staThread.Start();
                        _mxAccessClient = new MxAccessClient(_staThread, _mxProxy, _config.MxAccess, _metrics);
                        _mxAccessClient.ConnectAsync(_cts.Token).GetAwaiter().GetResult();

                        // Step 6: Start monitor loop
                        _mxAccessClient.StartMonitor();
                    }
                    catch (Exception ex)
                    {
                        Log.Warning(ex, "MxAccess connection failed — continuing without runtime data access");
                        _mxAccessClient?.Dispose();
                        _mxAccessClient = null;
                        _staThread?.Dispose();
                        _staThread = null;
                    }
                }

                // Step 7: Create GalaxyRepositoryService → TestConnection
                _galaxyStats = new GalaxyRepositoryStats { GalaxyName = _config.OpcUa.GalaxyName };

                if (_galaxyRepository != null)
                {
                    var dbOk = _galaxyRepository.TestConnectionAsync(_cts.Token).GetAwaiter().GetResult();
                    _galaxyStats.DbConnected = dbOk;
                    if (!dbOk)
                        Log.Warning("Galaxy repository database connection failed — continuing without initial data");
                }

                // Step 8: Create OPC UA server host + node manager
                var effectiveMxClient = (IMxAccessClient?)_mxAccessClient ?? _mxAccessClientForWiring ?? new NullMxAccessClient();
                _serverHost = new OpcUaServerHost(_config.OpcUa, effectiveMxClient, _metrics);

                // Step 9-10: Query hierarchy, start server, build address space
                if (_galaxyRepository != null && _galaxyStats.DbConnected)
                {
                    try
                    {
                        var hierarchy = _galaxyRepository.GetHierarchyAsync(_cts.Token).GetAwaiter().GetResult();
                        var attributes = _galaxyRepository.GetAttributesAsync(_cts.Token).GetAwaiter().GetResult();
                        _galaxyStats.ObjectCount = hierarchy.Count;
                        _galaxyStats.AttributeCount = attributes.Count;

                        _serverHost.StartAsync().GetAwaiter().GetResult();
                        _nodeManager = _serverHost.NodeManager;

                        if (_nodeManager != null)
                        {
                            _nodeManager.BuildAddressSpace(hierarchy, attributes);
                            _galaxyStats.LastRebuildTime = DateTime.UtcNow;
                        }
                    }
                    catch (Exception ex)
                    {
                        Log.Warning(ex, "Failed to build initial address space");
                        if (!_serverHost.IsRunning)
                        {
                            _serverHost.StartAsync().GetAwaiter().GetResult();
                            _nodeManager = _serverHost.NodeManager;
                        }
                    }
                }
                else
                {
                    _serverHost.StartAsync().GetAwaiter().GetResult();
                    _nodeManager = _serverHost.NodeManager;
                }

                // Step 11-12: Change detection wired to rebuild
                if (_galaxyRepository != null)
                {
                    _changeDetection = new ChangeDetectionService(_galaxyRepository, _config.GalaxyRepository.ChangeDetectionIntervalSeconds);
                    _changeDetection.OnGalaxyChanged += OnGalaxyChanged;
                    _changeDetection.Start();
                }

                // Step 13: Dashboard
                _healthCheck = new HealthCheckService();
                _statusReport = new StatusReportService(_healthCheck, _config.Dashboard.RefreshIntervalSeconds);
                _statusReport.SetComponents(effectiveMxClient, _metrics, _galaxyStats, _serverHost);

                if (_config.Dashboard.Enabled)
                {
                    _statusWebServer = new StatusWebServer(_statusReport, _config.Dashboard.Port);
                    _statusWebServer.Start();
                }

                // Step 14
                Log.Information("LmxOpcUa service started successfully");
            }
            catch (Exception ex)
            {
                Log.Fatal(ex, "LmxOpcUa service failed to start");
                throw;
            }
        }

        public void Stop()
        {
            Log.Information("LmxOpcUa service stopping");

            try
            {
                _cts?.Cancel();
                _changeDetection?.Stop();
                _serverHost?.Stop();

                if (_mxAccessClient != null)
                {
                    _mxAccessClient.StopMonitor();
                    _mxAccessClient.DisconnectAsync().GetAwaiter().GetResult();
                    _mxAccessClient.Dispose();
                }
                _staThread?.Dispose();

                _statusWebServer?.Dispose();
                _metrics?.Dispose();
                _changeDetection?.Dispose();
                _cts?.Dispose();

                AppDomain.CurrentDomain.UnhandledException -= OnUnhandledException;
            }
            catch (Exception ex)
            {
                Log.Warning(ex, "Error during service shutdown");
            }

            Log.Information("Service shutdown complete");
        }

        private void OnGalaxyChanged()
        {
            Log.Information("Galaxy change detected — rebuilding address space");
            try
            {
                if (_galaxyRepository == null || _nodeManager == null) return;

                var hierarchy = _galaxyRepository.GetHierarchyAsync().GetAwaiter().GetResult();
                var attributes = _galaxyRepository.GetAttributesAsync().GetAwaiter().GetResult();

                _nodeManager.RebuildAddressSpace(hierarchy, attributes);

                if (_galaxyStats != null)
                {
                    _galaxyStats.ObjectCount = hierarchy.Count;
                    _galaxyStats.AttributeCount = attributes.Count;
                    _galaxyStats.LastRebuildTime = DateTime.UtcNow;
                    _galaxyStats.LastDeployTime = _changeDetection?.LastKnownDeployTime;
                }
            }
            catch (Exception ex)
            {
                Log.Error(ex, "Failed to rebuild address space");
            }
        }

        private static void OnUnhandledException(object sender, UnhandledExceptionEventArgs e)
        {
            Log.Fatal(e.ExceptionObject as Exception, "Unhandled exception (IsTerminating={IsTerminating})", e.IsTerminating);
        }

        // Accessors for testing
        internal IMxAccessClient? MxClient => (IMxAccessClient?)_mxAccessClient ?? _mxAccessClientForWiring;
        internal PerformanceMetrics? Metrics => _metrics;
        internal OpcUaServerHost? ServerHost => _serverHost;
        internal LmxNodeManager? NodeManagerInstance => _nodeManager;
        internal ChangeDetectionService? ChangeDetectionInstance => _changeDetection;
        internal StatusWebServer? StatusWeb => _statusWebServer;
        internal StatusReportService? StatusReportInstance => _statusReport;
        internal GalaxyRepositoryStats? GalaxyStatsInstance => _galaxyStats;
    }

    /// <summary>
    /// Null implementation of IMxAccessClient for when MXAccess is not available.
    /// </summary>
    internal sealed class NullMxAccessClient : IMxAccessClient
    {
        public ConnectionState State => ConnectionState.Disconnected;
        public int ActiveSubscriptionCount => 0;
        public int ReconnectCount => 0;
        public event EventHandler<ConnectionStateChangedEventArgs>? ConnectionStateChanged;
        public event Action<string, Vtq>? OnTagValueChanged;

        public System.Threading.Tasks.Task ConnectAsync(CancellationToken ct = default) => System.Threading.Tasks.Task.CompletedTask;
        public System.Threading.Tasks.Task DisconnectAsync() => System.Threading.Tasks.Task.CompletedTask;
        public System.Threading.Tasks.Task SubscribeAsync(string fullTagReference, Action<string, Vtq> callback) => System.Threading.Tasks.Task.CompletedTask;
        public System.Threading.Tasks.Task UnsubscribeAsync(string fullTagReference) => System.Threading.Tasks.Task.CompletedTask;
        public System.Threading.Tasks.Task<Vtq> ReadAsync(string fullTagReference, CancellationToken ct = default) => System.Threading.Tasks.Task.FromResult(Vtq.Bad());
        public System.Threading.Tasks.Task<bool> WriteAsync(string fullTagReference, object value, CancellationToken ct = default) => System.Threading.Tasks.Task.FromResult(false);
        public void Dispose() { }
    }
}